Lead wire construction and method of sealing



Oct. 9, 1951 H. K. ISHLER LEAD WIRE CONSTRUCTION AND METHOD OF SEALINGFiled July 12, 1946 m m m m Harry/fennei'b 19/216) "ya/M @ZMZLW I I HisHfl'orney Patented Oct. 9, 1951 LEAD WIRE CONSTRUCTION AND METHOD OFSEALING Harry Kenneth Ishlcr, Floral Park, N. Y., assignor to SylvaniaElectric Products, Inc., a corporation of Massachusetts Application July12, 1946, Serial No. 682,998

. 6 Claims. (Cl. I'M-65.5)

The present invention relates to hermetically sealed devices havingconductors sealed through the envelope thereof. More particularly theinvention is directed to a method of sealing metalto-glass, and also theform of seal resulting from practicing the method.

In vacuum-tight devices, such as electron tubes and the like, it hasalways been a problem to seal satisfactorily the lead-in wire throughthe envelope during the manufacture of the device. This problem iscomplicated by the type of the device, the character of sealing-in wirerequired, the form of the seal made, etc. Presses and headers containinga plurality of leads are commonly fabricated before the general assemblyof the device, as for example an electron tube, and the sealingoperation in the fabrication of such parts is relatively simple. On theother hand, individual lead-in wires are customarily sealed separatelythrough some particular portion of the envelope of the device, as forexample they may be brought out through the side or top, and terminatein a tip formed externally during the sealing operation. The failure oftip seals is relatively high because the tip. enerally pointed, isinherently weak. Mechanical strains, such as may be produced by bendingthe lead-in wire in handling or installing the tube, frequently crackthe tip withthe result that the vacuum of the tube is broken, therebyrendering the tube defective.

Another source of sealing-in shrinkage in the production of vacuum-tightdevices is the burning or melting of lead-in wires during the sealingoperation. The art requires the use of high-- speedautomatic machineryand in performing various operations, such as exhaust and sealingofi,time is the essence. It is therefore a practical requirement that tipseals be made rapidly which necessitates the use of relatively intenseheat to melt quickly the glass or material of the envelope. Under theseconditions the lead-in wire heats rapidly and may burn or melt beforethe seal is formed. Various expedients have been proposed to overcomethis difficulty. For example, using a. lead-in wire of larger diameterthan would otherwise be desired; also using special sealing-inconductors requiring special glasses. These expedients introducecomplications and have not been a satisfactory solution to the problem.

Among the objects of the invention are: to provide a method and meanswhereby the leadin wire is protected from injury that may be caused byexcessive heat applied during the sealing-in of the lead through theenvelope of a vacuum-tight device; to avoid the formation of a sealhaving a pointed tip which renders the seal inherently fragile; tostrengthen the tip of that type seal; to relieve mechanical strains atthe exit of the lead-in wire from the envelope of the device, whichstrains may be produced by manipulation of the lead-in wire; to providea sealing-in construction which permits the formation of a seal betweenthe envelope material and a leading-in wire, and simultaneously theformation of a tight joint or union between protective means for theleading-in wire, the lead and protective means being brought out throughthe tip; and other novel features of construction which will becomeapparent as the description proceeds.

Referring to the drawings:

Fig. 1 is a side elevation, partly in section, of an electron tubeembodying the seal construction contemplated by the present invention;

Fig. 2 is a sectional view along the line 2-2 of Fig. 1;

Fig. 3 is a fragmentary side elevation, partly in section, of the topportion of the tube shown in exhaust and sealing position;

Fig. 4 shows the structure of Fig. 3 at the completion of the exhaustand sealing operation; and

Fig. 5 is a side elevation of a full-size completed electron tube.

The invention is shown embodied in an electron tube of the miniaturetype in order to afford a complete understanding of the variousstructural features contemplated, and also the method of practicing theinvention, although it will be appreciated that such a device is usedfor purposes of illustration only. Referring to Fig. 1

it will be, seen that the tube may comprise an elongated tubularenvelope l, enclosing an electron assembly indicated generally by thenumeral 2. The assembly 2 may comprise a conventional arrangement ofelectrodes, support members and lead-in wires, such as for example acentral cathode surrounded by a plurality of grids and an anode, whichelements are supported between mica discs. Connection to the electrodesof the assembly are made principally by lead-in wire 3 sealed through aheader 4, which is prefabricated as a unit and closes the bottom of theenvelope of the tube.

According to present day construction of miniature tubes they do nothave a base in the usual sense of the term, but rather connections tothe associated apparatus are made directly to the leading-in wires ofthe tube. Another characteristic feature of conventional miniature tubesis the absence of leading-in wires brought out through the side or topof the tube envelope, although this is common practice in themanufacture of relatively large vacuum-tight devices. The principalreason why this practice has not been extended to the construction ofminiature tubes is because a seal made with the side or top of theenvelope, results in the formation of a pointed tip and this point isinherently fragile unless protected by the usual cap provided in thecase of relatively large tubes. Furthermore, where a cap is provided forthe tip of the seal, the lead-in wire is connected to the cap which thenbecomes a terminal for connecting the tube in the circuit.

It has not been found practical to adopt this practice to themanufacture of miniature tubes for the reasons just explained, as wellas for other reasons obvious to those skilled in the art. Therefore, asstated above, among the objects of the invention it is proposed toprovide a seal having a reinforced tip which construction may beutilized in the production of miniature tubes.

The sealing-in construction contemplated by the invention for makingconnection to an electrode, particularly through the top of the tube,comprises a sub-assembly including a sealing-in conductor or lead-inwire having a surrounding sheath or sleeve 9 slidably mounted thereon.The sleeve 8 consists of an elongated tubular body of non-conducting andpreferably friable material, such as ceramic, which sleeve closely fitsthe lead-in wire 5 but provides enough clearance to be actuated bygravity as presently explained. As shown in Figs. 1 and 4, one end ofthe lead-in wire 5 is connected, as by welding, to a loop 3, which inturn is connected to the anode of the electrode assembly 2, while theother end of the wire 5 extends into an exhaust tube 1, which latter iseventually consolidated into a seal having a tip 6.

When the tube is in an upright position, as shown in Fig. 1, the ceramicsleeve or sheath 9 slides by force of gravity to the bottom of thelead-in conductor 5 and rests against the loop 8. When the tube is inthis position the header 4 may be sealed to the envelope 1. Forexhausting and sealing-01f purposes the position of the tube is inverted(see Figs. 3 and 4) and connection with the exhaust pumps is made bymeans of exhaust tube 1. With the tube in the position shown in Fig. 3,the air may be pumped out through the exhaust tube 1, the parts may beheated to drive out absorbed gases, the cathode may be activated byraising its temperature, and any other required steps may be performed,this process usually being carried out on automatic machinery.

At the completion of the exhaust process, the seal to lead wire I ismade by melting the exhaust tube so that the material thereof, forcedinward by the external air pressure, flows around the lead wire 5,simultaneously sealing the lead and closing the envelope, as presentlyexplained.

The sealing fires (schematically illustrated) are applied opposite thesleeve 9, which being of ceramic, prevents the lead wire 5 fromoverheating and melting during the sealing operation. By preventingexcessive heating of the lead-in wire 5 it is possible to employ a leadwire of smaller diameter than otherwise would be possible. This hasadvantages obvious to workers of the art. The length of the ceramicsleeve 9 and the location of a stop or support II, which may take iiform of a short sleeve or a flattened surface on. the lead wire I, areso chosen that the ceramic sleeve I is properly positioned with respectto the point at which the sealing fires are applied.

Further advantages of the use of a ceramic sleeve arise from the way inwhich the seal is formed, as shown in Fig. 4. The material of theexhaust tube flows around the wire 5 and also around the ceramic sleeve8 so that the ceramic sleeve is embedded in the seal and becomes a partof the tip, the exhaust tube material making a close joint wtih thesleeve as well as sealing to the lead wire.

After the seal has been formed, a portion of the tip, with the adjoiningembedded section of the sleeve 0, is cut away or broken on at itspointed end, leaving the completed tube as shown in Fig. 5. This may bedone with a pair of pliers or by automatic means, and is feasiblebecause both the material of the envelope and the sleeve are friable, i.e., one is glass and the other ceramic.

The lead-in wire 5 thus emerges from the en v'elope via the sealed-inportion of the sleeve. 8, which portion forms a union with the sealand/or tip, and the lead-in wire 5 is not in contact with the tip at thepoint of emergence therefrom. Consequently, since the sleeve has anappreciably larger diameter than the lead wire, the bending of the leadwire, which is likely to occur during handling or installing of thetube, is not likely to crack the seal, especially the tip, thus avoidingor materially reducing a source of shrinkage by air leaking into thedevice. The breakage of tip seals 15 a serious shrinkage factor, andtherefore, any construction or technique which will materially reducethis form of shrinkage is an important advancement in the industry.

It will be clear to those skilled in the art that in the practice of theinvention many modifications may be made from the embodiment describedand illustrated. It is not necessary, for example, to exhaust the airfrom the device through an exhaust tube surrounding a lead-in wire; inaccordance with general practice there would be no exhaust operation inthe making of side seals. The support sleeve 9 may be composed of a widevariety of satisfactory materials. Additionally, the ceramic sleeve 9may be replaced by a suitable coating applied to the lead wire 5; forexample, a coating of aluminum oxide deposited on the lead byelectrophoresis has been used. This variation is possible because thecoatmg serves primarily as a protection to the lead-in wire and is notrelied upon for making the seal between the envelope and the sealing-inconductor.

Therefore, although I have shown and described a particular embodimentof my invention, I do not desire to be limited thereto, and I intend inthe appended claims to cover all modifications which do not depart fromthe spirit and scope of my invention.

What I claim is:

1. An electrical device comprising an envelope having a glass wall, afriable, heat-shielding sleeve, and a flexible conductor extendingthrough said wall and said sleeve, said glass wall being sealed to saidconductor and to said sleeve, and said sleeve extending to the exteriorof said en velope.

2. An electron discharge device comprising an envelope having a wall ofglass enclosing part of the length of a flexible conductor in a cavityof progressively reduced cross-section, said cavity terminating wherethe conductor is sealed to the glass, and an outwardly adjacent friablesleeve surrounding said conductor and sealed in the glass, saidconductor extending beyond the end of said sleeve.

3. An electron discharge device comprising an envelope having a wall ofglass enclosing part of the length of aconductor within a cavity ofprogressively reduced cross-section, said cavity terminating where theconductoris sealed to the glass, and an outwardly adjacent sleeveloosely surrounding said conductor and sealed in the glass.

4. In the manufacture of electron discharge devices, the method ofcompleting the envelope comprising the steps of arranging an electrodeconductor having a fixed stop and a friable loosely surroundingheat-shielding sleeve extending along part of it length within anexhaust tubulation extending from the incomplete envelope, fusing theexhaust tubulation while vertical and with the sleeve resting on thestop to form glass seals to the conductor and the sleeve,

protective sleeve surrounding the conductor, said sleeve having one endimbedded in the seal at the side of the seal to the exterior of theenvelope and said conductor extending from said sleeve.

6. An electron discharge device having an envelope including a glasswall, said envelope having a seal-off tip and a conductor sealed throughsaid tip and extending to the exterior of the envelope, the thickness ofglass about said conductor diminishing toward the end of the tip and afriable sleeve surrounding the portion of said conductor which isimbedded in the end of said tip. I

HARRY KENNETH ISHLER.

REFERENCES crrEn The following references are of record in the file ofthis patent;

UNITED STATES PATENTS Number Name Date 475,998 Burnett et al May 31,1892 690,953 Hewitt Jan. 14, 1902 1,320,114 Birdsall Oct. 28, 19191,489,099 Reynolds Apr. 1, 1924 2,060,043 Cox Nov. 10, 1936 2,084,913Kaufieldt June 22, 1937 2,147,418 Bahls Feb. 14, 1939 2,169,570 RonciAug. 15, 1939 2,201,717 Dawihl et al. May 21, 1940 2,202,337 Cohn May28, 1940 2,248,644 Reger et a1 July 8, 1941 2,276,218 Lemmens Mar. 10,1942 2,292,863 Beggs Aug. 11, 1942 2,296,579 Seelen Sept. 22, 19422,447,158 Cartun Aug. 17, 1948 2,486,101 Beggs Oct. 25, 1949 2,496,303Morse et a1 Feb. 7, 1950 FOREIGN PATENTS Number Country Date 476,488England Dec. 6, 1937 512,974 England Sept. 29, 1939' 577,738

England May 29, 1948

